Push contents of X86TargetInfo::setFeatureEnabled down to a static function called by the virtual version and all the places in getDefaultFeatures. This way getDefaultFeatures doesn't make so many virtual calls.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190847 91177308-0d34-0410-b5e6-96231b3b80d8